Possessed ][+ Mainboard

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Possessed ][+ Mainboard

Here's an anecdote to take to the bank. I have a Rev D ][+ board that was previously damaged and malfunctioned. A while back, I restored it, tested it, did a full burn in, RAM tests, the lot, and it passed them all. I put it into a static bag and put it on a shelf. 

 

Today, when I was putting a board in a system, I selected that one first, as I had marked it 'Restored, 100%, 48K'. After I completely installed the board, I powered it up, and.... Screen of rubbish characters. Might be the 9334, but my point in all of this, is that I did not first bench test it again ere installing it. IDK what would have gone bad in two months sitting on a shelf, but I marked the bag 100% burn in verified--and this board had some suspect issues originally where it had phantom problems that some standard chip swaps seemed to cure. 

 

The takeaway, is even if you tested something two months earlier, test it again ere spending the time installing it. 

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Shelf time is cruel sometimes

Shelf time is cruel sometimes.

I've run into that situation more than once.  I suspect that it miche be socket or cold-solder joint related.  Or maybe a flakey 9334, who knows?

 

I've got a Microsoft 16K card that doesn't work at all when it's cold. The computer doesn't even recognize that it's there.

Within a minute it's recognized but fails.  Over the next minute or so RAM tests performed show fewer and fewer errors until the errors disappear.

Once it's allowed to warm up for evan 3 minutes it works perfectly and passes every single test I can throw at it.

 

I've been chasing that one for weeks, but since I can only test it when it's stone cold my testing windows are extremely short.

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Sounds like internal IC breakdown

Sounds like internal IC breakdown such as the lead weld to the actual silicone internal to the IC has given up the ghost.  Likely makes connection with thermal expansion.  My guess anyway.

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macnoyd wrote:Sounds like
macnoyd wrote:

Sounds like internal IC breakdown such as the lead weld to the actual silicone internal to the IC has given up the ghost.  Likely makes connection with thermal expansion.  My guess anyway.

Very probably an issue that dissipates with heat. Pretty sure that this is what you are pointing toward, and it may likely be this. It's just annoying. 

 

I suppose, that if I solve this, I might post about it, but it isn't high up on my prior5ity list. I more or less simply wanted to share my little anecdote and move on. I have three ][/][+ boards not in cases: One I know is fine, the second (the board in question), I thought was fine, and the third is a misfit Rev 4 board that needs a lot of reworking. I spent one good working board to make me Beltron functional, until I can diagnose and repair the Beltron mainboard, if that ever occurs. 

 

I need one for a B&H, but I expect this to be the story of these boards. Every system that I have had, maintained, or worked on since it was new never had any issues and works as new to this day. Everything that I receive as trade or buy 'as-is' is horribly broken. 

 

This isn't some sort of 'help me' topic. It is more or less me venting about stupid things, such as not triple-checking the working status of a board ere spending an hour installing it. If I had more members on the Apple 77 Discord server, I would have posted it there, but people (for whatever reason) join that, then leave b/c there isn't activity; b ut the only way to generate activity is for people to sign up and post. I suppose that it doesn't appeal as much as forums, and that part, I understand. 

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I am starting to hate this

I am starting to hate this board. Working perfectly, failed, working perfectly, failed in another way. The CPU is not running (no beep, random RAM on screen), and I am starting to think it might be the NE555 or the Q5 transistor; or the LS02 at A12, but until I fix my oscope or get another one, I am using this cheap chinese multifunction digital probe that likes to power itself off after two minutes, which suffice to say, is particularly irritating. 

 

I need to invest in a 74xx series IC tester, so that I know if the ICs that are on the PCB, or if the ICs that I am using to swap in are good or not. All of the RAM that I am using tested good, but until I have samples of bad 4116s to check if the tester finds internal faults, IDK if I can trust it. (I did try several other 6502s and none changed a thing, so I doubt that the CPU itself is dead unless I am cooking each one that I tested. I suppose I can test the CPU on a known good board next for now. 

 

I have some //e KBs to finish, so I will work on those this week and decide if it is worth investing more time on these boards or if they are to become donors for the future. I would have liked to kept one ][ or ][+ board as a loose PCB for my bench, but if not, fine. 

 

I am pretty sure that a bad 9334 cannot cause a no beep situation, ever. If I am mistaken, feel free to correct me, but I am out of spares for that part, and I have stolen a lot of them off of Disk ][ cards, so I need to resupply. 

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I don't think the 9334 would

I don't think the 9334 would cause that issue - it's used for video mode switching.

Probably it's one of the video shift registers that aren't switching properly.

 

The TL866-II IC programmer works pretty well for testing a lot of 74-series logic chips.

Here's the list from the product website (http://www.autoelectric.cn/EN/index.html)

      4000            4001            4002            4007                  4009            4010            40106           4011                  4012            4013            4015            4016                  40161           40162           4017            40174                 40175           4018            4019            40193                 4022            4023            4024            4025                  4026            4027            4028            4029                  4030            4031            4034            4040                  4041            4042            4043            4044                  4048            4049            4050            4051                  4053            4066            4067            4068                  4069            4070            4071            4072                  4073            4075            4076            4077                  4078            4081            4082            4093                  4099            4501            4503            4506                  4510            4511            4512            4514                  4515            4518            4519            4520                  4529            4532            4543            4572                  6821            7400            7401            7402                  7403            7404            7405            74HC05(OD)            7406            74HC06(OD)      7407            74HC07(OD)            7408            7409            7410            74107                 74109           7411            74112           74113                 7412            74123           74125           74126                 7413            74132           74133           74136                 74137           74138           74139           7414                  74140           74147           74148           74149                 7415            74151           74153           74154                 74157           74158           7416            74160                 74161           74162           74163           74164                 74165           74166           7417            74173                 74174           74175           7418            74181                 74182           74190           74191           74192                 74193           74194           74195           7420                  7421            7422            74237           74240                 74241           74242           74243           74244                 74245           7425            74251           74253                 74257           74258           74259           7426                  74260           74266           7427            74273                 7428            74280           74283           74292                 74293           74294           74298           74299                 7430            7432            7433            74354                 74356           74365           74366           74367                 74368           7437            74373           74374                 74375           74377           7438            74386                 74390           74393           744053          7440                  7442            7447            7450            7451                  7452            74533           74534           74540                 74541           7455            74563           74564                 74573           74574           7458            74589                 74595           74597           7460            7461                  7462            74640           74643           74646                 74648           7465            74688           747266                7473            7474            7475            7476                  7485            7486            7490            7492                  7493            7497            8155            8255                  8259            8279           

And if you're willing to pay just a bit more to get one really fast you cna order it from Amazon.

It sucks at programing 2716s but it's dirt cheap and does a lot of other programmable ICs fairly well.

 

 

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That happens to me with my

That happens to me with my Apple II and II+ boards. I don't use them regularly, but every few years I pull them out and usually none of them work right. Typically just working chips around in the sockets makes it work again for a while. Rinse and repeat.

 

I think it's the ROM sockets typically, but sometimes others. It's just oxidation...

 

Entropy gets all electronics (and us) over time.

 

 

 

 

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